Calculating electric flux when given a charge (Gauss)

[Will12]

Homework Statement

A charge Q=5.14 nC
is located at the center is located at the center of a Gaussian sphere of radius R=10.0 cm
. The sphere lies within a uniform upward electric field E=2100 NC
The net outward electric flux through the sphere is What?

Second problem (bonus round!)
A closed Gaussain cube of side length d=10.0cm contains two charges q1=-14uc q2=28uc placed at different locations within the cube (never given a specific placement) what it the net outward flux?

Homework Equations

ξοΦ=qenc
E=q/4πξοr^2 (maybe?)

The Attempt at a Solution

I've tried solving both of these problems but keep getting them wrong and don't know what I'm doing wrong
Problem one
Φ=5.14E-9 C/ξο
Then since the other flux makes a net zero it shouldn't come into play right? or do I need to use the electrostatic force equation and that's also my flux?

Problem two.
I've tried gauss' law after finding the net enclosed charge but that's been wrong every time, I don't even know what equation to start this with, do I need to find the electro static force for each charge first and then add them together so they each cancel in part then do the equation with
ξο∫E*dA?

Thanks for any help you can give me

 

[NFuller]

Problem one
Φ=5.14E-9 C/ξο
Then since the other flux makes a net zero it shouldn't come into play right?

Your answer is correct, unless this problem is not in vacuum such that $\epsilon$ is different.

Problem two.
I've tried gauss' law after finding the net enclosed charge but that's been wrong every time, I don't even know what equation to start this with, do I need to find the electro static force for each charge first and then add them together so they each cancel in part then do the equation with

This uses the same method as problem 1. Who/What is telling you that this is wrong?

 

[Will12]

Your answer is correct, unless this problem is not in vacuum such that $\epsilon$ is different.

This uses the same method as problem 1. Who/What is telling you that this is wrong?

Orion Personalized practice marks it wrong every time, maybe its a rounding tolerance issue or something else. Ill have to play with it a little more I guess

 

[NFuller]

Orion Personalized practice marks it wrong every time, maybe its a rounding tolerance issue or something else.

There must be something wrong with how you are entering the answer. I know some of these programs have a funny way of entering numbers in scientific notation. Try to check that in the help section on Orion.

 

[SammyS]

Orion Personalized practice marks it wrong every time, maybe its a rounding tolerance issue or something else. Ill have to play with it a little more I guess

Is a numerical answer expected? What are the units? What did you use for $\ \varepsilon_0\$?

 

[Will12]

Is a numerical answer expected? What are the units? What did you use for $\ \varepsilon_0\$?

8.85E-12 is the value it gives in the book. units vary across problems but its always nc E-9 or uc E-6.

 

[SammyS]

8.85E-12 is the value it gives in the book. units vary across problems but its always nc E-9 or uc E-6.

What are the Units for electric flux ?

 

[Will12]

What are the Units for electric flux ?

Newtons*Meter^2/Coulombs

 

[SammyS]

Newtons*Meter^2/Coulombs

Correct.

Did you include these in your answer, or were they provided by Orion Personalized practice ?

 

[Will12]

Correct.

Did you include these in your answer, or were they provided by Orion Personalized practice ?

They are provided. Also I've just learned that I can turn on them giving the correct answer after problem completion and they give it in 12345.123456789 format, and don't list a tolerance for rounding anywhere, but have been accepting rounding to one decimal in other portions of the program, In fact I was able to complete the entire cilindrical semitry portion of the program without a single wrong answer using the same online calculator with the same value of Eo and rounding to one decimal place so I don't know what's going wrong

 

[SammyS]

They are provided. Also I've just learned that I can turn on them giving the correct answer after problem completion and they give it in 12345.123456789 format, and don't list a tolerance for rounding anywhere, but have been accepting rounding to one decimal in other portions of the program, In fact I was able to complete the entire cilindrical semitry portion of the program without a single wrong answer using the same online calculator with the same value of Eo and rounding to one decimal place so I don't know what's going wrong

What is the numerical answer that you are entering? How many significant digits should it have ?

 

[Will12]

What is the numerical answer that you are entering? How many significant digits should it have ?

For the problem listed above my answer was 580.790 But it doesn't say how may significant figures it wants, or gives a rounding tolerance.

 

[SammyS]

For the problem listed above my answer was 580.790 But it doesn't say how may significant figures it wants, or gives a rounding tolerance.

Have you not studied significant figures in your course ?

 

[Will12]

Have you not studied significant figures in your course ?

We have but previously have been instructed regardless of significant figures given by the problem to give three, or one, dependent on which system we were using. Because each system last semester was programed slightly differently and would reject your answers if you were outside of their parameters.

 

[vela]

For the problem listed above my answer was 580.790 But it doesn't say how may significant figures it wants, or gives a rounding tolerance.

Are you confusing decimal places and sig figs? If you entered 580.790, you're supplying an answer with 6 sig figs, and that's why it's getting marked wrong.